In the US, Toxoplasma Gondi is the second leading cause of food borne mortality and more than 60 million people are persistently infected with this organism and this infection is a concern in many patients with primary or acquired defects in T cell mediated immunity. Due to the ease of transmission and its ability to cause severe disease, T. Gondi is classified as a Class B Biodefense pathogen. The initial interaction between Toxoplasma and host macrophages and dendritic cells is key in determining the outcome of this infection and this parasite can inject proteins into uninfected host cells that are thought to antagonize their ability to control infection. Using novel transgenic parasites combined wth unique mouse strains and advanced imaging technologies we are now able to identify these injected but uninfected populations and propose experiments to determine whether these events affect the innate host response or the development of the adaptive response required for long term control of T. gondii.